The Puzzling Paradox of Sign Language
It takes longer to sign words than to say them. So how is it possible to sign and speak at the same rate?
Here’s a curious paradox related to American Sign Language, the
system of hand-based gestures used by around 2 million deaf people in
the US and elsewhere to communicate.
Almost 40 years ago, researchers discovered that although it takes
longer to make signs than to say the equivalent words, on average
sentences can be completed in about the same time. How can that be
possible?
Today, Andrew Chong and buddies at Princeton University in New
Jersey give us the answer. They say that the information content of
the 45 handshapes that make up sign language is higher than the
information content of phonemes, the building blocks of the spoken
word. In other words, there is greater redundancy in spoken English
than signed English.
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In a way, that’s a trivial explanation, a mere restatement of the
problem. What’s impressive about the Princeton contribution is the
way they have arrived at this conclusion.
The team has determined the entropy of American Sign Language
experimentally, by measuring the frequency of handshapes on video
logs for deaf people uploaded to youtube.com, deafvideo.tv and
deafread.com as well as from video recordings of signed conversations
taken on campus.
It turns out that the information content of handshapes is on
average just 0.5 bits per handshape less than the theoretical
maximum. By contrast, the information content per phoneme in spoken
English is some 3 bits lower than the maximum.
This raises an interesting question. The spoken word has all this
redundancy for a reason: it allows us to be understood over a noisy
channel. Lessen the redundancy and your capacity to deal with noise
is correspondingly reduced.
Why would sign language need less redundancy? “Entropy might
be higher for handshapes than English phonemes because the visual
channel is less noisy than the auditory channel…so error correction
is less necessary,” say Chong and co.
They go on to speculate that signers cope with errors in an
entirely different way to speakers. “Difficulties in visual
recognition of handshapes could be solved by holding or slowing the
transition between those handshapes for longer amounts of time, while
difficulties in auditory recognition of spoken phonemes cannot always
be easily solved by speaking phonemes for longer amounts of time,”
they say.
And why is all this useful? Chong and friends say that if sign
language is ever to be encoded and transmitted electronically, a
better understanding of its information content will be essential for
developing encoders and decoders that do the job. A worthy pursuit by
any standards.
Ref: arxiv.org/abs/0912.1768: Frequency of Occurrence and Information Entropy of American Sign Language
